The Effect of Root Exudate 7,4\u27-Dihydroxyflavone and Naringenin on Soil Bacterial Community Structure

Our goal was to investigate how root exudate flavonoids influence the soil bacterial community structure and to identify members of the community that change their relative abundance in response to flavonoid exudation. Using a model system that approximates flavonoid exudation of Medicago sativa roots, we treated a soil with 7,4′-dihydroxyflavone and naringenin in two separate experiments using three different rates: medium (equivalent to the exudation rate of 7,4′-dihydroxyflavone from M. sativa seedlings), high (10× the medium rate), and low (0.1× the medium rate). Controls received no flavonoid. Soil samples were subjected to ATP assays and 16S rRNA gene amplicon sequencing. The flavonoid treatments caused no significant change in the soil ATP content. With the high 7,4′-dihydroxyflavone treatment rate, operational taxonomic units (OTUs) classified as Acidobacteria subdivision 4 increased in relative abundance compared with the control samples, whereas OTUs classified as Gaiellales, Nocardioidaceae, and Thermomonosporaceae were more prevalent in the control. The naringenin treatments did not cause significant changes in the soil bacterial community structure. Our results suggest that the root exudate flavonoid 7,4′-dihydroxyflavone can interact with a diverse range of soil bacteria and may have other functions in the rhizosphere in addition to nod gene induction in legume—rhizobia symbiosis

The Effect of Root Exudate 7,4'-Dihydroxyflavone and Naringenin on Soil Bacterial Community Structure.

Our goal was to investigate how root exudate flavonoids influence the soil bacterial community structure and to identify members of the community that change their relative abundance in response to flavonoid exudation. Using a model system that approximates flavonoid exudation of Medicago sativa roots, we treated a soil with 7,4'-dihydroxyflavone and naringenin in two separate experiments using three different rates: medium (equivalent to the exudation rate of 7,4'-dihydroxyflavone from M. sativa seedlings), high (10× the medium rate), and low (0.1× the medium rate). Controls received no flavonoid. Soil samples were subjected to ATP assays and 16S rRNA gene amplicon sequencing. The flavonoid treatments caused no significant change in the soil ATP content. With the high 7,4'-dihydroxyflavone treatment rate, operational taxonomic units (OTUs) classified as Acidobacteria subdivision 4 increased in relative abundance compared with the control samples, whereas OTUs classified as Gaiellales, Nocardioidaceae, and Thermomonosporaceae were more prevalent in the control. The naringenin treatments did not cause significant changes in the soil bacterial community structure. Our results suggest that the root exudate flavonoid 7,4'-dihydroxyflavone can interact with a diverse range of soil bacteria and may have other functions in the rhizosphere in addition to nod gene induction in legume-rhizobia symbiosis

Non-metric multidimensional scaling (NMS) ordination plots.

<p>(A) 7,4′-Dihydroxyflavone experiment, (B) naringenin experiment. Points represent samples, crosses are group centroids. Samples of the same treatment are enclosed in convex hulls. Stress is calculated on a scale of 0 to 100. (Treatments: ● high, ♦ medium, ■ low, and ▲ control).</p

Experimental warming and fire alter fluxes of soil nutrients in sub-alpine open heathland

Climatic changes in the Australian Alps are likely to raise mean ambient temperatures, decrease precipitation and increase the frequency of fires, which together are likely to affect soil nutrients. Changes in the availability of soil nutrients are in turn expected to influence plant growth and community composition. In alpine soils of the southern hemisphere, it is unknown how the interaction between warming and fire will affect nutrient availability and to what extent changes will resemble global trends. We used open-top chambers and ion-exchange membranes to examine the effects of warming and fire on the cumulative flux of available nutrients and toxic elements in soil of a sub-alpine heathland during the final 2 yr of a 9 yr passive warming and post-fire experiment at sites on the Bogong High Plains, Victoria, Australia. Compared to unwarmed plots, experimental warming increased NH₄⁺, H₂PO₄⁻, Na⁺ and K⁺, and decreased Mg²⁺, Ca²⁺, Al³⁺ and soil moisture. Increased N and P are consistent with changes in alpine soils of the northern hemisphere, but the effect of warming on other elements has not been reported. A consistent decrease in Al³⁺ availability with warming has implications for carbon turnover and invasion by exotic species. Fire increased Al³⁺ availability and decreased Mn²⁺ availability, indicating a change in potentially toxic elements in burnt areas. Warming and drying changed the availability of all measured nutrients and resembled trends in the northern hemisphere, indicating that changes in the alpine and sub-alpine ecosystems of the Australian Alps, and globally, are probably inevitable.13 page(s